The present invention relates to a vacuum brake booster for motor vehicles comprising low pressure housing which is divided into a vacuum chamber and working chamber by a rigid partition movable together with a control hub. Channels are arranged in the control hub for air guiding to connect the hollow interior chamber of the control hub, which contains a valve arrangement controlling the air guiding or flow, to the vacuum chamber and the working chamber.
From French Pat. No. 2,118,925 a vacuum brake booster has become known, in which the partition positively butts against a shoulder around the circumference of the control hub and is secured by a clamping circlip in its position at the control hub. The control hub, furthermore, embraces coaxially to the valve arrangement the force transmitting element in such a way that the reaction disc arranged on the force transmitting element is opposite the valve piston with a small clearance between reaction disc and valve piston.
The control hub projects out of the working chamber of the vacuum brake booster and is opened to the atmosphere. Furthermore, the interior chamber of the control hub is connected to the working chamber via radial openings and to the vacuum chamber via air guiding channels which are disposed at an angle of approximately 45 degrees to the axis of the control hub.
The valve arrangement is designed in such a way that it, being controllable by the piston bar of the operating device leading into the control hub, connects the working chamber to the vacuum chamber (resting position), or to the atmosphere (working position), or closes the air guiding channel to the working chamber (operational position).
In an embodiment having this type of the air guiding channels in the control hub leading to the vacuum chamber, the production requires a lot of material and is expensive. In addition the control hub must have grooves in order to secure the valve piston from the outside and must have an interior chamber designed in such a way that a sealing edge is created for the valve arrangement.
Furthermore, the air guiding channels are critical areas regarding stress created by the transmission of the vacuum forces.